TABLE 1.
Characteristics of included studies
| First author [reference] | Country | Setting | Design | Study period | COVID-19 positive | Age (years) | Male (n) | Current smokers (n) | COPD (n) | Diabetes (n) | Hypertension (n) | NOS score (out of 9) | ||
| Asthma (n) | Overall (n) | Mean | Median | |||||||||||
| Ahlström [ 17 ] | Sweden | Mixed | Case–control study | 6 March to 27 May 2020 | 133 | 1981 | 61 | 1465 | 75 | 522 | 982 | 9 | ||
| Almazeedi [ 41 ] | Kuwait | Hospital | Retrospective cohort study | 24 February to 20 April 2020 | 43 | 1096 | 41 | 888 | 44 | 5 | 155 | 177 | 9 | |
| Arslan [ 46 ] | Turkey | Hospital | Retrospective cohort study | 18 March to 15 May 2020 | 58 | 767 | 51.99 | 374 | 80 | 43 | 137 | 220 | 8 | |
| Ashinyo [ 47 ] | Ghana | Hospital | Retrospective cohort study | 23 March to 29 June 2020 | 24 | 307 | 37.9 | 174 | 20 | 219 | 7 | |||
| Aveyard [ 13 ] | Mexico | Hospital | Retrospective cohort study | 27 February to 21 June 2020 | 4942 | 178 306 | 44.1 | 88 083 | 8 | |||||
| Baumer [ 12 ] | UK | Hospital | Prospective cohort study | 9 March to 7 May 2020 | 12 | 52 | 54.82 | 29 | 8 | |||||
| Bergman [ 18 ] | Sweden | Mixed | Case–control study | To mid-September 2020 | 4493 | 68 575 | 46 | 26 808 | 2168 | 4897 | 16 416 | 9 | ||
| Beurnier [ 48 ] | France | Hospital | Prospective cohort study | 15 March to 15 April 2020 | 37 | 112 | 60 | 49 | 17 | 32 | 9 | |||
| Calmes [ 49 ] | Belgium | Hospital | Retrospective cohort study | 18 March to 17 April 2020 | 57 | 596 | 58.75# | 294 | 9 | |||||
| Castilla [ 19 ] | Spain | Mixed | Retrospective cohort study | July to December 2020 | 2330 | 35 387 | 38.8 | 17 172 | 6119 | 1404 | 1893 | 4543 | 9 | |
| Chhiba [ 50 ] | USA | Hospital | Retrospective cohort study | 1 March to 15 April 2020 | 220 | 1526 | 53.3# | 654 | 43 | 9 | ||||
| Choi [ 20 ] | South Korea | Mixed | Retrospective cohort study | To 15 May 2020 | 218 | 7372 | 44.5# | 3000 | 9 | |||||
| Dennis [ 30 ] | UK | Hospital | Retrospective cohort study | 1 March to 27 July 2020 | 1557 | 17 606 | 67 | 10 560 | 231 | 421 | 9 | |||
| Eggert [ 51 ] | USA | Hospital | Retrospective cohort study | 1 March to 30 September 2020 | 598 | 5596 | 38.4 | 2635 | 123 | 88 | 609 | 1021 | 9 | |
| Emami [ 52 ] | Iran | Hospital | Retrospective cohort study | 20 February to 1 March 2020 | 25 | 1239 | 51.48 | 692 | 27 | 176 | 7 | |||
| Ferastraoaru [ 53 ] | USA | Hospital | Retrospective cohort study | 14 March to 27 April 2020 | 951 | 4558 | 60.5 | 9 | ||||||
| Fong [ 54 ] | UK | Hospital | Retrospective cohort study | 1 March to 31 May 2020 | 102 | 617 | 65 | 9 | ||||||
| Garcia-Pachon [ 14 ] | Spain | Community | Retrospective cohort study | 3 March to 12 April 2020 | 10 | 376 | 54 | 192 | 8 | |||||
| Green [ 21 ] | Israel | Mixed | Retrospective cohort study | February to June 2020 | 153 | 2266 | 33.31 | 1200 | 102 | 200 | 276 | 9 | ||
| Guan [ 55 ] | China | Hospital | Retrospective cohort study | December 2019 to 6 May 2020 | 244 | 39 420 | 55.7 | 19 655 | 9 | |||||
| Gude-Sampedro [ 22 ] | Spain | Mixed | Retrospective cohort study | 6 March to 7 May 2020 | 288 | 10 454 | 58 | 4172 | 258 | 180 | 619 | 1457 | 9 | |
| Gupta [ 29 ] | USA | Hospital | Retrospective cohort study | To 4 March 2020 | 30 | 529 | 70 | 286 | 39 | 36 | 289 | 416 | 6 | |
| Hansen [ 23 ] | Denmark | Mixed | Retrospective cohort study | 1 February to 10 July 2020 | 354 | 5104 | 54.6 | 2399 | 432 | 598 | 9 | |||
| Ho [ 38 ] | USA | Hospital | Retrospective cohort study | 7 March to 7 June 2020 | 468 | 10 523 | 58.35 | 5707 | 286 | 1679 | 2662 | 9 | ||
| Je [ 56 ] | Australia | Hospital | Retrospective cohort study | March to April 2020 | 22 | 197 | 45 | 94 | 4 | 8 | 28 | 7 | ||
| Kim [ 57 ] | South Korea | Hospital | Case–control study | February to May 2020 | 66 | 2200 | 56.71 | 785 | 92 | 30 | 378 | 645 | 9 | |
| Kipourou [ 58 ] | Kuwait | Hospital | Prospective cohort study | 24 February to 27 May 2020 | 235 | 3995 | 40.4 | 2814 | 140 | 17 | 730 | 778 | 9 | |
| Lee [ 15 ] | South Korea | Community | Retrospective cohort study | January to 27 May 2020 | 686 | 7272 | 45.3 | 2927 | 1041 | 1401 | 9 | |||
| Lemus Calderon [ 59 ] | Spain | Hospital | Retrospective cohort study | To July 2020 | 577 | 6310 | 59 | 2983 | 873 | 1641 | 3239 | 9 | ||
| Liao [ 60 ] | USA | Hospital | Retrospective cohort study | 11 March to 23 June 2020 | 41 | 113 | 50 | 53 | 2 | 57 | 11 | 18 | 9 | |
| Lieberman-Cribbin [ 61 ] | USA | Hospital | Retrospective cohort study | 29 February to 24 April 2020 | 272 | 6245 | 57 | 3060 | 8 | |||||
| Lombardi [ 62 ] | Italy | Hospital | Retrospective cohort study | 20 February to 20 April 2020 | 20 | 1043 | 52.5# | 704 | 9 | |||||
| Louie [ 24 ] | Australia | Mixed | Case series | 19 March to 15 May 2020 | 10 | 99 | 54 | 51 | 2 | 8 | 14 | 8 | ||
| Lovinsky-Desir [ 63 ] | USA | Mixed | Prospective cohort study | 11 February to 7 May 2020 | 163 | 1298 | 52 | 762 | 55 | 9 | ||||
| Martos-Benítez [ 25 ] | Mexico | Mixed | Retrospective cohort study | 1 January to 12 May 2020 | 1188 | 38 324 | 46.9 | 22 362 | 3277 | 889 | 7168 | 8340 | 9 | |
| Mash [64] | South Africa | Hospital | Retrospective cohort study | March to June 2020 | 67 | 1376 | 46.3 | 571 | 95 | 50 | 364 | 564 | 8 | |
| Mather [65] | USA | Hospital | Case–control study | February to November 2020 | 88 | 1045 | 64.6 | 352 | 18 | 221 | 307 | 8 | ||
| Murillo-Zamora [66] | Mexico | Hospital | Retrospective cohort study | 4 March to 15 August 2020 | 1448 | 66 123 | 52.4 | 40 124 | 2619 | 21 840 | 26 728 | 9 | ||
| Nystad [26] | Norway | Mixed | Retrospective cohort study | 1 March to 13 May 2020 | 515 | 7632 | 33.22# | 161 | 468 | 977 | 7 | |||
| Patone [27] | UK | Mixed | Retrospective cohort study | 1 November to 26 January 2021 | 29 792 | 198 420 | 37.7 | 93 765 | 22 134 | 1873 | 10 347 | 19 636 | 9 | |
| Robinson [67] | USA | Hospital | Case–control study | 4 March to 2 July 2020 | 562 | 3248 | 51 | 911 | 131 | 321 | 107 | 8 | ||
| Rosenthal [68] | USA | Hospital | Retrospective cohort study | March to May 2020 | 105 | 727 | 49.46 | 165 | 278 | 8 | ||||
| Salacup [69] | USA | Hospital | Retrospective cohort study | 1 March to 24 April 2020 | 18 | 242 | 66 | 123 | 30 | 118 | 180 | 8 | ||
| Schönfeld [28] | Argentina | Mixed | Retrospective cohort study | 3 March to 2 October 2020 | 12 580 | 207 079 | 41 | 103 487 | 4074 | 4405 | 20 058 | 39 833 | 9 | |
| Shah [70] | USA | Hospital | Retrospective cohort study | 3 February to 31 March 2020 | 4 | 33 | 63 | 22 | 0 | 1 | 9 | 16 | 8 | |
| Tutiya [71] | Brazil | Hospital | Retrospective cohort study | 13 March to 7 June 2020 | 7 | 114 | 32.4 | 0 | 12 | 13 | 7 | |||
| Valverde-Monge [72] | Spain | Hospital | Retrospective cohort study | 31 January to 17 April 2020 | 113 | 2539 | 62.66 | 1275 | 154 | 89 | 403 | 1054 | 9 | |
| Wang [40] | China | Hospital | Retrospective cohort study | 28 January to 25 February 2020 | 68 | 562 | 47 | 265 | 8 | |||||
| Yang [37] | South Korea | Community | Retrospective cohort study | 1 January to 15 May 2020 | 725 | 7340 | 47.1 | 2970 | 350 | 951 | 1638 | 9 | ||
| Yordanov [16] | France | Mixed | Prospective cohort study | March to August 2020 | 814 | 7320 | 43 | 2301 | 790 | 87 | 402 | 978 | 6 | |
| Zhang [31] | China | Hospital | Retrospective cohort study | 29 December 2019 to 16 February 2020 | 1 | 290 | 57 | 155 | 10 | 6 | 27 | 81 | 8 | |
COVID-19: coronavirus disease 2019; NOS: Newcastle–Ottawa Scale. #: imputed values based on weighted average.